This invention relates generally to the protection of wire ropes from corrosive conditions and more particularly to the sealing of wire ropes against corrosive environments by the use of plastic compositions including plastic foam compositions.
Various expedients have in the past been used to bar the entrance of water and moisture into the interior of wire ropes and strands. Such expedients have included the use of heavy lubricants, external plastic coatings and the encapsulation of individual wires, strands or even an entire wire rope in solid plastic sheaths. Lubricants are soon lost from an otherwise unprotected strand or rope while external protective coatings are subject to wear and upon rupture at any point will admit moisture to the interior of the rope or strand. Solid encapsulation, on the other hand, seriously interferes with the flexibility of the rope or strand and is, furthermore, difficult to attain.
U.S. Pat. Nos. 3,681,911 and 3,778,994 to D. V. Humphries and 3,800,522 to C. R. Hughes et al as well as several other recently issued patents disclose a successful alleviation of many of these previous problems. In these disclosures a working wire rope or a single working strand is impregnated with a liquid plastic composition during fabrication and said liquid is then converted to a flexible foam by the application of heat. The foam material is adherent to the individual wires and because of its cellular structure has a minimal effect on the flexibility of the rope or strand. The exterior of the rope or strand may be covered with a thin layer of the plastic foam or with a layer of denser unfoamed plastic or may more preferably be wiped clean, particularly in working ropes and strands, i.e. those which are used over sheaves and pulleys and the like or otherwise used in dynamic operations as opposed to static use such as guy lines and other types of permanent anchor lines. The bare wire surfaces resist abrasion and wear in these cases while the interior foam material between the individual wires, which preferably closely encloses all but the outer surfaces of the wires, prevents the access of water and moisture to the interior surfaces of the wires.
Where the rope or strand is used in static applications such as for guy lines and the like, it may be desirable to encapsulate the entire foam plastic filled rope or strand within a denser outer plastic sheath which may be applied by an extrusion operation or the like. Encapsulated plastic foam impregnated rope and strand is also useful for some working ropes and strands. The outer extruded sheath provides additional abrasion and corrosion resistance dependent upon the material of the sheath and also provides a smooth exterior surface on the rope or strand, which surface when formed with a smooth extrusion die opening forms a very desirable uniform sealing surface when a seal must be formed between the surface of the rope and some other object which the rope or strand contacts, for example, in passing through a wall or bulkhead or the like. The interior plastic foam material, on the other hand, prevents moisture and other corrosion inducing agents from gaining entrance to the interior of the rope or strand and being trapped within the interior if the outer plastic sheath is damaged by abrasion or the like.
Extruded external plastic sheaths have various disadvantages among which are the cost of the extrusion operation, additional stiffness of the rope or strand covered with a uniform tubular outer sheath, possible looseness of the sheath on the underlying rope causing sliding and wear when the extruded sheath is formed on a working rope and other disadvantages. The foremost disadvantage of an extruded sheath over the surface of a foam impregnated wire strand is the cost of the extra extrusion operation and the fact that a pressure type extrusion must be used if a uniform smooth outer surface is to be applied to the surface of a wire rope.